It is well known that radiation generated by circuitry operating at high frequencies can cause interference with radio and television broadcasts, a phenomenon which is called radio frequency interference (RFI). To prevent RFI the circuitry may be enclosed in an electrically conductive housing. For example, in a mobile radio telephone the circuitry of the transceiver is commonly contained within a conductive housing comprising an open-topped box and a separate lid for closing the box. To prevent RF radiation escaping from the housing it is important for there to be an effective and continuous RFI seal between the lid and the box.
FIG. 1 shows in cross-section a part of a prior art transceiver housing comprising an open-topped box 1 and a lid 2. The sealing means comprises a compressible conductive 0-ring gasket 3 made, for example, of a metal braid with a sponge rubber core. The gasket 3 is seated in a channel 4 located in the top face of side wall 5 of the box 1. In use, the lid 2 is fastened down to the box 1, e.g. using screws, thus compressing the gasket 3 and forming continuous electrical contact (and hence an effective RF seal) between the lid and the box.
This prior art transceiver housing does, however, have drawbacks. Firstly, the side wall of the box has to be sufficiently wide to accommodate the sealing gasket 3. Consequently the side wall has to be made thicker than would otherwise be necessary. This necessitates the use of more material for manufacturing the box, which therefore increases the cost, and also results in the box occupying more space. Secondly, the gasket adds further to the expense of the overall housing and, being a separate component, requires an additional step in the assembly of the housing.
Another prior art transceiver housing employing a different RFI sealing means is illustrated in FIG. 2. In this case a series of electrically conductive leaf spring contacts 6 attached to the lid 2, e.g., by rivets 7, bear against the internal face of the side walls 5 of the box 1 (see FIG. 2A). The leaf springs 6 are suitably formed as a unitary comb-like member as shown in plan view in FIG. 2B. In the case of a rectangular housing four such comb-like members 8 would be used, one along each of the four sides of the lid 2. This housing arrangement has the advantage that it occupies less space, since the side walls of the box can be made thinner, but manufacture is more costly because of the extra material for the springs and assembly is more difficult and time consuming because of the requirement to attach the individual comb-like members 8 to the lid 2.
WO 83/01174 discloses as prior art a two-part housing for radio frequency circuitry comprising an open-topped box made of, for example cast aluminium and a cover plate made of a resilient material such as cold rolled steel. The cover plate includes integral rectangular-shaped flange projections bent at approximately 90.degree. with respect to the plane of the cover plate. The flange projections are shaped with an elbow or ridge which makes electrical contact against the inside walls of the box when the cover plate is press fitted into the opening in the box, thus providing effective RFI sealing. This arrangement relies on the resilience of the flange projections.